Devices and methods for determining blood flow around a body lumen

ABSTRACT

A system may include an expandable member, and a plurality of sensors disposed on an outer surface of the expandable member and circumferentially spaced apart from one another, wherein each of the plurality of sensors includes a first emitter configured to emit light of a first wavelength, and a detector configured to detect light, and a controller coupled to the plurality of sensors.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This patent application claims the benefit under 35 U.S.C. § 119 to U.S.Provisional Patent Application No. 62/522,168, filed on Jun. 20, 2017,the entirety of which is incorporated herein by reference.

TECHNICAL FIELD

Implementations of the present disclosure relate to devices and methodsfor determining blood flow around a body lumen, and more specifically,an indicator for identifying inflamed regions of the gastrointestinaltract.

INTRODUCTION

Inflammatory Bowel Disease (IBD) is a disease that progresses from themucosal lining of the small bowel or/and colon through the entirebowel/colon wall. Currently, the use of magnetic resonance imaging (MRI)slices as a non-invasive imaging technique for diagnosing IBD is limitedby resolution, and does not provide real-time blood flow. Coherencetomography (CT) is another approach, but is not suitable for patientswith certain gastrointestinal diseases because the requirement formultiple imaging sessions over time increases the risk of cancer for thepatient. Other challenges include subjective severity in scoring fromdoctor to doctor, diagnosis through elimination, increased patient riskfor cancer due to monitoring progression with repetitive CT-scans, andthe unavailability of and lack of standardization associated with colorenhanced ultrasound.

SUMMARY

In one implementation, the disclosure is directed to a system includingan expandable member, and a plurality of sensors disposed on an outersurface of the expandable member and circumferentially spaced apart fromone another, wherein each of the plurality of sensors includes a firstemitter configured to emit light of a first wavelength, and a detectorconfigured to detect light, and a controller communicatively coupled tothe plurality of sensors. The controller may be configured to, from atleast one detector, receive along a first short vector, a measurement oflight intensity over time of light, reflected off of body tissue, at thefirst wavelength and originating from a first emitter from a samesensor; from at least one detector, receive along a first long vector, ameasurement of light intensity over time of light, reflected off of bodytissue, at the first wavelength and originating from a first emitterfrom a circumferentially adjacent sensor; calculate separate perfusionindexes corresponding to measured light intensity over time of eachfirst short vector and each first long vector; and initiate the displayof the separate perfusion indexes corresponding to measured lightintensity over time of each first short vector and each first longvector.

Each of the plurality of sensors may include a second emitter configuredto emit light of a second wavelength that is different than the firstwavelength, wherein the controller is further configured to from eachdetector, receive along a second short vector, a measurement of lightintensity over time of light, reflected off of body tissue, at thesecond wavelength and originating from a second emitter from a samesensor; from each detector, receive along a second long vector, ameasurement of light intensity over time of light, reflected off of bodytissue, at the second wavelength and originating from a second emitterfrom a circumferentially adjacent sensor; calculate separate perfusionindexes corresponding to each second short vector and each second longvector; and cause the display of the calculated separate perfusionindexes corresponding to each second short vector and each second longvector. The second emitter may be configured to emit light of a thirdwavelength different than the first wavelength and the secondwavelength, wherein the controller is further configured to: from eachdetector, receive along a third short vector, a measurement of lightintensity over time of light, reflected off of body tissue, at the thirdwavelength and originating from a second emitter from a same sensor;from each detector, receive along a third long vector, a measurement oflight intensity over time of light, reflected off of body tissue, at thethird wavelength and originating from a second emitter from acircumferentially adjacent sensor; calculate separate perfusion indexescorresponding to each third short vector and each third long vector; andcause the display of the calculated separate perfusion indexescorresponding to each third short vector and each third long vector. Thecontroller may be further configured to, from each detector, receivealong two third long vectors, measurements of light intensity over timeof light, reflected off of body tissue, at the third wavelength andoriginating from second emitters of two different circumferentiallyadjacent sensors. The third wavelength may be infrared light. Thecontroller may be further configured to, from each detector, receivealong two second long vectors, measurements of light intensity over timeof light, reflected off of body tissue, at the second wavelength andoriginating from second emitters of two different circumferentiallyadjacent sensors. The second wavelength may be visible red light. Thecontroller may be further configured to, from each detector, receivealong two first long vectors, measurements of light intensity over timeof light, reflected off of body tissue, at the first wavelength andoriginating from first emitters of two different circumferentiallyadjacent sensors. The first wavelength may be visible green light. Thesystem may include an ECG assembly coupled to the controller andconfigured to measure ECG signals. The controller may be furtherconfigured to: while calculating each perfusion index, synchronize intime, measured light intensity from each vector with a measurement fromthe ECG assembly to determine pulse transit time and perfusionintensity; and use the pulse transit time and the perfusion intensity tocalculate a respective perfusion index corresponding to each vector. Thecontroller may be configured to receive a measurement of light intensityover time along only one first short vector or first long vector at anygiven time. The plurality of sensors may include four circumferentiallyspaced apart sensors. Each detector may be longitudinally aligned witheach other detector. Each first emitter may be longitudinally alignedwith each other first emitter.

In another implementation, the disclosure is directed to a method fordetermining blood flow surrounding a body lumen, the method comprising:receiving, at separate times with a detector: a measurement of lightintensity over time of light, reflected off of body tissue, at a firstwavelength and originating from an emitter from a sensorcircumferentially aligned with the detector; and a measurement of lightintensity over time of light, reflected off of body tissue, at the firstwavelength and originating from an emitter from a sensorcircumferentially offset from the detector; calculating separateperfusion indexes corresponding to each measurement; and displaying theseparate perfusion indexes.

In yet another implementation, the disclosure is directed to a methodfor determining blood flow surrounding a body lumen using a plurality ofsensors, the method comprising: receiving, with a detector at eachsensor, a measurement of light intensity over time of light, reflectedoff of body tissue, at a first wavelength and originating from a firstemitter from a same sensor as the detector; receiving, with a detectorat each sensor, a measurement of light intensity over time of light,reflected off of body tissue, at a first wavelength and originating froma first emitter from a sensor circumferentially adjacent to thedetector; calculating separate perfusion indexes based on eachmeasurement; and displaying the separate perfusion indexes.

The body lumen may be in a gastrointestinal tract. Only one measurementmay be received at any given time. Each measurement may be taken whilethe plurality of sensors are in a same location within the body lumen.

In yet another implementation, the disclosure is directed to a medicaldevice including a catheter; an optical sensor disposed at or adjacentto a distal end of the catheter, the optical sensor including aphotodetector and one or more emitters, the photodetector and each ofthe one or more emitters of the optical sensor being disposed linearlyalong a longitudinal axis of the catheter; and a controller disposedwithin the catheter, the controller being configured to determine athickness of tissue adjacent to the optical sensor based on input fromthe optical sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate various implementations andtogether with the description, serve to explain the principles of thedisclosed implementations.

FIG. 1 is a schematic view of a perfusion measurement system, accordingto an implementation of the present disclosure.

FIG. 2 is a perspective view of an expandable member with a plurality ofoptical sensors.

FIG. 3 is a front view of an optical sensor.

FIG. 4 is a side view of the expandable member of FIG. 2 with aplurality of optical sensors.

FIG. 5 is a flowchart of a method, according to an implementation of thedisclosure.

FIG. 6A is illustration of an electrocardiogram measured by the systemof FIG. 1.

FIG. 6B is an illustration of a photoplethysmogram measured by thesystem of FIG. 1.

FIG. 7 is a depiction of the electrocardiogram of FIG. 6A and thephotoplethysmogram of FIG. 6B on common axes.

FIG. 8 is an illustration of a perfusion index created using opticaldata measured by the system of FIG. 1.

FIG. 9 is an illustration of tissue thickness created using optical datameasured by the system of FIG. 1.

FIG. 10 is a perspective view of an expandable member and a plurality ofsensors, according to another implementation of the present disclosure.

FIG. 11 is a perspective view of an expandable member and a plurality ofsensors, according to yet another implementation of the presentdisclosure.

FIGS. 12 and 13 show un-deployed and deployed configurations,respectively, of an expandable member and a plurality of sensors,according to yet another implementation of the present disclosure.

FIG. 14 is a perspective view of an optical sensor according to anotherimplementation of the present disclosure.

FIG. 15 is a side view of the optical sensor of FIG. 14.

FIG. 16 is a top view of a portion of the optical sensor of FIG. 14.

FIG. 17 is an illustration of a timing sequence of a photodetector and aplurality of emitters from the optical sensor of FIG. 14.

FIG. 18 is a fitted line plot regression of an experiment using anoptical sensor.

DETAILED DESCRIPTION

Reference will now be made in detail to implementations of the presentdisclosure, which are illustrated in the accompanying drawings. Whereverpossible, the same reference numbers will be used throughout thedrawings to refer to the same or like parts or components. The term“distal” refers to the direction that is away from the user or operatorand into the patient's body. By contrast, the term “proximal” refers tothe direction that is closer to the user or operator and away from thepatient's body. In the discussion that follows, relative terms such as“about,” “substantially,” “approximately,” etc. are used to indicate apossible variation of ±10% in a stated numeric value.

Implementations of the present disclosure may provide a low-cost imagingsolution for determining the severity of various gastrointestinaldiseases. In some implementations, the data collected and displayed to aphysician or clinician may be robust enough to enable differentiation ofulcerative colitis from Chrohn's disease.

Referring to FIG. 1, a system 100 may include a catheter 102, anelectrocardiogram (ECG) lead assembly 104, controller 106, and a fluiddelivery device 108.

Catheter 102 may extend from a proximal end 110 toward a distal end 112,and may include an expandable member 114 at or adjacent distal end 112.Expandable member 114 may be a compliant or semi-compliant balloonconfigured to inflate and deflate via a fluid conveyed by fluid deliverydevice 108. In other implementations, expandable member 114 could be anexpandable mesh or an expandable basket with a plurality of radiallyexpandable basket legs. As explained in further detail below, one ormore sensors may be coupled to expandable member 114 for measuring bloodflow, pressure (e.g., pressure sensor 118), and/or impedance within agastrointestinal tract of a patient. Pressure sensor 118 may beconfigured to measure pressure within expandable member 114, and tomeasure intra-abdominal pressure (IAP) within the body lumen whenexpandable member 114 is deflated. In embodiments where expandablemember 114 is a balloon, pressure sensor 118 may be integral orotherwise coupled to an inflating pump. In embodiments where expandablemember 114 is a mesh, a miniature integrated MEMS sensor may be used tomeasure pressure, and could be placed in the same plane as one or moreoptical sensors. Controller 106 may evaluate signals from pressuresensor 118 to control inflation and deflation of expandable member 114,so as not to cause any vascular restriction or accidental occlusion.Pressure sensor 118 also could be used to determine safe placement ofstents. Increasing expansion while reading perfusion intensity mayresult in a temporary and substantial decrease in perfusion. Thus,pressure readings from sensor 118 can be used to reduce expansion inthese instances to ensure safe delivery by determining whether expansionof the stent causes a temporary restriction of blood flow.

ECG lead assembly 104 may be coupled to controller 106, and may beconfigured to sense an ECG signal based on electrical activity of thepatient's heart sensed by one or more electrodes 120. While ECG leadassembly 104 is shown in FIG. 1 with four electrodes 120, any othersuitable number of electrodes 120 may be utilized.

Controller 106 may include a processor that is generally configured toaccept information from the system and system components, and processthe information according to various algorithms. The processor may be adigital IC processor, analog processor or any other suitable logic orcontrol system that carries out the control algorithms. In someimplementations, controller 106 may record treatment parameters such as,e.g., sensor data, so that they may be accessed for concurrent orsubsequent analysis. Controller 106 may include software that provides auser interface to components within the system. The software may enablea user (e.g., clinician) to configure, monitor, and control operation ofcatheter 102, ECG lead assembly 104, and control circuitry and pumpcomponents within fluid delivery device 108. As described in furtherdetail below, the software may be configured to process a signalindicative of blood flow within a gastrointestinal tract to calculate anarea indicative of a blood flow rate within the gastrointestinal tract.

Fluid delivery device 108 may include a pump, and may be configured todeliver fluid to and convey fluid from expandable member 114 to inflateand deflate expandable member 114. Fluid delivery device 108 may becontrolled by controller 106, or another suitable controller. The pumpmay be any suitable pump, such as, e.g., a peristaltic pump, pistonpump, motorized pump, infusion pump, or the like. Fluid delivery device108 may be powered by electrical power, mechanical power, chemicalpower, or another suitable mechanism. Fluid delivery device 108 mayinclude a source (e.g., a reservoir of liquid or a canister of gas) usedto inflate and deflate the expandable member 114.

Referring to FIGS. 1-4, one or more sensors 116 may be disposed on anouter surface of expandable member 114. In one implementation, foursensors 116 may be circumferentially spaced about expandable member 114about 90 degrees from one another, although other numbers of sensorsand/or different spacing arrangements also are contemplated. Sensor 116may be configured to generate a signal that can be used by controller106 to determine blood flow, e.g., perfusion, within a gastrointestinaltract of a patient. Sensor 116 may include a first emitter 135, a secondemitter 136, and a detector 137. First emitter 135 and second emitter136 each may be configured to emit light, e.g., non-visible infraredlight and/or visible light toward body tissue. For example, firstemitter 135 and second emitter 136 each may include one or more lightemitting diodes (LEDs). In some implementations, first emitter 135 andsecond emitter 136 may be configured to direct different wavelengths oflight at tissue. For example, first emitter 135 may be configured todirect light of a first wavelength (e.g., red light with a wavelengthfrom about 620 nm to about 750 nm) toward body tissue, while secondemitter 136 may be configured to direct light of a second wavelengthdifferent than the first wavelength (e.g., green light from about 520 nmto about 540 nm, or at about 530 nm) toward body tissue. First emitter135 and/or second emitter 136 may be configured to separately orsimultaneously direct one or more wavelengths of light toward bodytissue. For example, first emitter 135 may be configured to directinfrared light (at a wavelength from about 700 nm to about 1 mm) inaddition to visible red light. Emitted light may be absorbed by the bodybased on the blood volume at the absorption location. Absorption occurswhen elements in the blood absorb photons and diffuse light passingthrough the blood. Hemoglobin, for example, is an absorber of light butabsorbs different light wavelengths at different rates. Backscatter isthe amount of light that is reflected back to the detector and is notabsorbed in the blood. Detector 137 may be a photodiode (e.g., a siliconphotodiode) that is configured to receive backscattered light reflectedfrom the body.

Each detector 137 may be longitudinally aligned (e.g., disposed at thesame longitudinal location) as each other detector 137. Similarly, eachfirst emitter 135 may be longitudinally aligned with each other firstemitter 135, and each second emitter 136 may be longitudinally alignedwith each other second emitter 136.

Referring to FIG. 3, detector 137 may be configured to measure reflectedlight that originates from an emitter (e.g., first emitter 135 and/orsecond emitter 136). For purposes of discussion herein, a short vectorrefers to reflected light detected by detector 137 that originated froman emitter on the same sensor 116 as the given detector 137. Thus,depending on the configuration of emitters on a given sensor, eachdetector 137 may be configured to detect light along one or more shortvectors. In one implementation, where first emitter 135 is configured toemit green light, and second emitter 136 is configured to emit red lightand infrared light, each detector 137 may be configured to detect lightalong three short vectors (green, red, infrared). Different absorptionrates in blood and tissue with known correlations can be used todetermine various physiological parameters (photoplethysmography), suchas, e.g., oxygen saturation, heart rate, perfusion intensity, surrogateblood pressure, and tissue thickness.

Referring to FIG. 4, a long vector refers to reflected light detected bydetector 137 that originated from an emitter on a circumferentiallyadjacent emitter. Thus, when a given sensor 116 is disposedcircumferentially between two other sensors 116, the detector 137 of thegiven sensor 116 may be configured to detect light from one or more longvectors from each of the two adjacent sensors (emitters). In theimplementation where first emitter 135 is configured to emit greenlight, and second emitter 136 is configured to emit red light andinfrared light, each detector 137 may be configured to detect lightalong six long vectors (three long vectors originating from each of thetwo circumferentially adjacent sensors 116).

In one implementation of the disclosure where four sensors 116 aredisposed around the circumference of expandable member 114, system 100may record measurements along a total of 36 vectors (12 short vectorsand 24 long vectors). Each of the four sensors 116 includes three shortvectors, totalling 12 short vectors. Additionally, each of the foursensors 116 includes six long vectors as set forth above, totalling 24long vectors. Devices with only one optical sensor may have a singlevector, which would not enable mapping of the blood vessels around thelumen, the determination of tissue thickness, or the data necessary tosize a stent during deployment.

Referring now to FIG. 5, an exemplary method 500 is shown. Method 500may begin at step 502, where sensors 116 and ECG assembly 104 may bedeployed. For example, catheter 102 may be orally inserted into apatient through the nose or mouth and into the gastrointestinal tractthrough the esophagus and stomach. Using fluoroscopic, ultrasonic,anatomic, or CT guidance, an endoscope (or expandable member 114 alone)may be positioned at a location (region of interest) within thegastrointestinal tract such as the duodenum. The region of interest thenmay be visualized using an imaging device (e.g., an endoscopic camera),and expandable member 114 may be extended to the region of interest viaa working port of the endoscope. Once expandable member 114 ispositioned at the location (region of interest), it may be expanded viafluid from fluid delivery device 108. Before, during, or after insertionof catheter 102 into the body, electrodes 120 of ECG lead assembly 104may be placed on a suitable site of a patient, such as the patient'schest, to monitor electrical activity of the heart. With expandablemember 114 and sensors 116 in position, all other light emitting sourcesin the body lumen, such as, e.g., a guiding light of an endoscope, maybe turned off to avoid interfering with measurements detected by sensor116.

Method 500 may proceed to step 504, where the system 100 may calibratesensors 116. At step 504, the required gains for detectors 137 and drivecurrents for the emitters 135 and 136 may be determined. In oneimplementation, calibration may be accomplished sequentially for eachsensor 116. Calibration for the short vector reflections of eachwavelength (e.g., red, infrared, and green) may take place for eachsensor 116. Each of the sensors 116 will be calibrated for each of itsshort vectors, and the values for the detector gain and current settingfor the emitters 135 and 136 may be stored. Then, each sensor 116 may becalibrated for its associated long vectors for each wavelength (e.g.,red, infrared, and green) for each circumferentially adjacent sensor.

The primary purpose of the calibration is to optimize the signal tonoise ratio received by detector 137. The secondary purpose is to obtainthe values of the gain and current settings for each vector, which arethen used as scoring factors in mapping out the tissue perfusion aroundthe body lumen.

After calibration, method 500 may proceed to step 506, where lightintensity measurements over time may be made continuously andsequentially for each of the 36 vectors. In some implementations, eachdetector 137 may be configured to perform more than one measurement at agiven time (e.g., pulse, blood oxygen, surrogate blood pressure, meanarterial pressure, perfusion intensity, tissue thickness). Controller106 may associate a time stamp to each measurement performed, or mayotherwise associate the time of day with each waveform collected by eachdetector 137. ECG lead assembly 104 may collect ECG data at all timesthat any detector 137 is collecting optical data.

After collecting data at step 506, method 500 may proceed to step 508,where the collected data may be analysed to generate a perfusion indexcorresponding to each vector at one or more wavelengths. Perfusion indexmay be the ratio of the pulsatile blood flow to the non-pulsatile staticblood flow. Perfusion index is an indication of pulse strength at themeasurement site, and may be indicative of tissue inflammation aroundthe measurement site. The perfusion index may be calculated based on adetermined perfusion intensity, which is a measure of blood velocity andits peak amplitude. The perfusion intensity may be determined using apulse transit time (PTT) and a height of an associated P wave. PTT isthe time it takes a pulse pressure (PP) waveform to propagate through alength of an arterial tree. The pulse pressure waveform results from theejection of blood from the left ventricle and moves with a velocity muchgreater than the forward movement of the blood itself. The P waverepresents atrial depolarization, which may result in atrialcontraction.

The data collected for each vector will be weighed against thecalibration values (gain and current), and used to create a perfusionintensity map. Higher gain settings and currents may be flagged assuspected low perfusion regions when looking at P wave heights. Theperfusion intensity map then may be manipulated to create a perfusionindex map.

The measured data from sensors 116 may be filtered using a suitablefilter, such as a High-Pass Finite Impulse Response (FIR) filter, toremove noise in the data, such as noise caused by distortion created bymechanical ventilation or intestinal peristalsis. For each vector, a PPGsignal 515 (FIG. 6A) and an ECG signal 516 (FIG. 6B) may synchronizedrelative to time at a suitable frequency, e.g., 100 Hz. Thissynchronization is illustrated in FIGS. 6A and 6B, which shows the PPGsignal 515 over time (FIG. 6A) for a given vector, and the correspondingECG signal 516 obtained at the same time.

The data based on the ECG signal 516 is used to determine an R wavesignal. Controller 106 may determine the R wave signal using aderivative based algorithm. Referring to FIG. 6B, a graph is illustrateddepicting ECG signal 516 having determined R waves marked with theletter R. R waves may be used as a trigger to identify PTT. The PTT maybe calculated as the time of flight from the R wave of the ECG signal516 to an associated P wave of PPG signal 515 (see FIGS. 6A, 6B, and 7).

Referring back to FIG. 6A, an area 600 under PPG signal 515 may becalculated. This area may represent the volume of pulse as a part of theintensity calculation. The PPG signal 515 is searched between twoconsecutive R waves, which are used to determine a time window in whichto search for a minimum value (shown as “A” in FIG. 6A) of a segment ofthe PPG signal 515. The minimum point A on the PPG signal 515 within thetime window after the R wave is used as the starting point of a PPGsegment. The ending point of the PPG segment is where the next minimumpoint of the PPG signal is detected (shown as A′ in FIG. 6A), which isalso a starting point for the next PPG segment. To calculate AC area600, a boundary line 602 is drawn between minimum points A and A′ on thePPG curve. AC area 600 may be the area below PPG signal 515, aboveboundary line 602, and between minimum points A and A′.

Once area 600 is determined for each vector, a perfusion intensityI_(Perf) may be calculated by dividing the AC area 600 (pulse area) foreach vector by the PTT of the same vector. To create the perfusionindex, perfusion intensity I_(Perf) may be normalized for all 36 vectorsas each may have different gain and current settings. Additionally, itis expected that the 24 long vectors will require higher current andgain settings than the short vectors. Short vector perfusion intensitiesmay be calculated and compared separately from perfusion intensities ofthe longer vectors. A short vector perfusion index (SV_Index_(n)) foreach of the 12 short vectors may be calculated using the followingequation:

${SV\_ Index}_{n} = \frac{I_{{Perf}_{n}}}{{GAIN}_{n}{xI}_{{LED}_{n}}}$

I_(LEDn) represents a current associated with a respective LED. Anormalization (k) will be made between short and long vectors to createa normalized scoring index. Longer vectors require more current to get areading that is at an acceptable level above a signal to noise ratio(SNR), and possibly require more gain. k may act as a scaling factor tocompensate the larger gain and current settings. Determination of k mayrequire empirical testing in some examples, and may include a balancebetween the short vector I_Perfn settings with the long vector I_Perf_nsettings, for example, where SV_I_PERF=LV_I_PERF. If the resultingintensity measurements are kept the same, k may be the ratio of gain andcurrent setting of long vectors over that of the short vectors.

The following equation may be used to calculate a long vector index(LV_Index_(m)), where k is used to scale the result so it is normalizedwith the short vectors.

${LV\_ Index}_{m} = {\frac{I_{{Perf}_{m}}}{{GAIN}_{m}{xI}_{{LED}_{m}}}k}$

The indexing score values may be represented as a radial map (see FIG.8), which when viewed (method step 510), gives a visual representationof perfusion index around the body lumen where the measurements weretaken with sensors 116. For illustration, a low perfusion is shownaround the SV_2 portion and adjacent long vectors.

For two wavelengths (e.g., green and red wavelengths), a variation ofthe Green's function of a diffusion into a substance can be used with aslope-ratio method to determine tissue wall thickness. The spectralratio of slopes shown in FIG. 9 represent the difference between shortvector perfusion to long vector perfusion of the green wavelength overthe difference of the short vector perfusion to long vector perfusion ofthe red wavelength.

${Ratio}{= \frac{{SV\_ Index}_{green} - {LV_{{Index}_{green}}}}{{SV\_ Index}_{red} - {LV\_ Index}_{red}}}$

This may be evaluated for each position around the sensor array. Thisratio may approximate tissue thickness surrounding a body lumen andsensor array. In the example having four optical modules around acircumference of an expandable member, there are two long vectors foreach short vector, and thus eight regional ratios. In some examples,slope tomography may be used to determine tissue wall thickness.

While the slopes used in some examples herein utilize multiplewavelengths of visible light (e.g., green and red), it other examples,combinations of visible and non-visible light may be used to determinetissue wall thickness, such as, e.g., green and IR, or red and IR.

After step 510, method 500 may return to step 502 for repositioning ofexpandable member 114 for additional measurements at different locationsin the body.

More complicated cases of Crohn's Disease, where a stricture may preventthe advancement of a scope/sensor array, may require extra steps ofdeploying a dilating device to open a passageway, and re-deploying thesensor array. FIGS. 10-13 show various “over-the-scope” devices withsensors 116 that can be used in these more complicated cases. Inparticular, FIG. 10 shows a system 1000 including an endoscopic device1002 extending from a proximal end (not shown) to a distal end 1003.Endoscopic device 1002 may be any suitable endoscopic member, such as,e.g., an endoscope, a ureteroscope, a nephroscope, a colonoscope, ahysteroscope, a uteroscope, a bronchoscope, a cystoscope, a sheath, or acatheter. Endoscopic device 1002 may include one or more additionallumens configured for the passage of a variety of tools and devices,including, but not limited to, imaging devices and tools for irrigation,vacuum suctioning, biopsies, and drug delivery. Endoscopic device 1002also may include an imaging device, e.g., a camera, at distal end 1003.

System 1000 may include a sensor assembly 1004 having an expandablemember 1006 disposed between a proximal cuff 1007 and a distal cuff1008. Proximal cuff 1007 and distal cuff 1008 each may extend around anexterior surface of endoscopic device 1002, and may be secured toendoscopic device 1002 by an interference fit or other suitablemechanism. Additionally, in system 1000, a distalmost end of distal cuff1008 may be positioned distal to a distalmost end of endoscopic device1002.

One or more sensors 116 may be disposed on an outer surface ofexpandable member 1006 in a substantially similar manner as describedabove with respect to sensors 116 and expandable member 114. In system1000, each sensor 116 may be coupled to a control member (e.g., controlwire) 1010 that is extended through a working channel of endoscopicdevice 1002 and connected at its proximal end to controller 106 (shownin FIG. 1). For example, control members 1010 may be bundled into asheath 1012, and sheath 1012 may be extended through the working channelof endoscopic device 1002. Distal portions of each control member 1010also may be positioned on an exterior surface of expandable member 1006and ultimately coupled with a given sensor 116. Similar to expandablemember 114, expandable member 1006 may be a compliant or semi-compliantballoon configured to inflate and deflate via a fluid conveyed by fluiddelivery device 108 (shown only in FIG. 1). Sheath 1012 also may includea lumen coupled to fluid delivery device 108 to convey fluid to and fromexpandable member 1006 for inflation and deflation. Alternatively,expandable member 1006 may be coupled to fluid delivery device 108 byanother mechanism.

A system 1100 is shown in FIG. 11, including a sensor assembly 1104positioned over endoscopic device 1002 (e.g., the same endoscopic devicedescribed with reference to FIG. 10). Sensor assembly 1104 may includean expandable member 1106 disposed between a proximal cuff 1107 and adistal cuff 1108. Proximal cuff 1107 and distal cuff 1108 each mayextend around an exterior surface of endoscopic device 1002, and may besecured to endoscopic device 1002 by an interference fit or othersuitable mechanism. Additionally, a distalmost end of distal cuff 1108may be positioned proximal to a distalmost end of endoscopic device1002.

One or more sensors 116 may be disposed on an outer surface ofexpandable member 1106. The arrangement of the sensors 116 on expandablemember 1106 may be similar to the arrangement of sensors 116 onexpandable member 1006 set forth above, except that control members 1010may be positioned entirely external to endoscopic device 1002. Forexample, control members 1010 may be bundled into a sheath 1112, andsheath 1112 may extend along the exterior of endoscopic device 1002.Similar to sheath 1012, sheath 1112 also may include a lumen coupled tofluid delivery device 108 (shown in FIG. 1) to convey fluid to and fromexpandable member 1106 for inflation and deflation.

A sensor assembly 1201 is shown in FIGS. 12 and 13 in un-deployed anddeployed configurations, respectively. Sensor assembly 1201 may becoupled to distal end 1003 of endoscopic device 1002, and may beconfigured to position one or more sensors 116 in contact with an innersurface 1222 of a body lumen 1220 (referring to FIG. 13). Sensorassembly 1201 may include a cuff 1202 having a proximal end 1203 and adistal end 1204. Cuff 1202 may slide onto distal end 1003 of endoscopicdevice 1002. Cuff 1202 may include one or more flexible arms 1208 thatare circumferentially spaced apart from one another. Each arm 1208 mayinclude a set curvature. For example, each arm 1208 may have a presetshape in a deployed configuration. As shown in FIGS. 12 and 13, each arm1208 may include a concave curvature when viewed from a perspectivedistal to the arm 1208, and may include a convex curvature when viewedfrom a perspective proximal to the arm 1208. Arms 1208 may be biasedinto either the un-deployed or deployed configuration.

Each of the one or more arms 1208 may include a mounted end 1209 and afree end 1210. Each of the one or more arms 1208 may be at leastpartially disposed in a corresponding recess 1211 in cuff 1202. Thus,each recess 1211 may be circumferentially offset from each other recess1211 of cuff 1202. Mounted end 1209 of each arm 1208 may form a hinge1212 with cuff 1202. Arms 1208 may move from a first, un-deployedposition, where free end 1210 is disposed proximally of mounted end1209, to a second, deployed position, where free end 1210 is disposeddistally of mounted end 1209. Arms 1208 may be moved between the firstand second positions by manipulating endoscopic device 1002 to causefree ends 1210 to engage with tissue. For example, distal movement ofendoscopic device 1002 may cause tissue of a body lumen to pushproximally against free ends 1210, moving arms 1208 into theconfiguration shown in FIG. 12. On the contrary, proximal movement ofendoscopic device 1002 causes tissue of the body lumen to push distallyagainst free ends 1210, moving arms 1208 into the configuration shown inFIG. 13. Thus, arms 1208 may be moved between un-deployed and deployedpositions by only passive mechanisms without any powered and/orautomated components. Alternatively, arms 1208 may be actively movedbetween the un-deployed and deployed configurations by an activemechanism, such as, e.g., a combination of motors, gears, and actuators.For example, a user may activate an actuator that causes a combinationof motors and gears to move arms 1208 between the un-deployed anddeployed positions. Furthermore, in one embodiment, each arm 1208 maylie flat/flush within a corresponding recess 1211, and an actuator mayrelease each arm 1208 when arms 1208 are positioned at a desired tissuesite.

A sensor 116 may be coupled to free end 1210 of each arm 1208. When arms1208 are in the first, un-deployed position shown in FIG. 12, theoptical components of sensors 116 may face radially inward toward acentral longitudinal axis 1230 of sensor assembly 1201, and may not beoperable. In the second, deployed position shown in FIG. 13, the opticalcomponents of sensors 116 may face radially outward away from centrallongitudinal axis 1230 and toward surface tissue 1222. Similar to thedevice shown in FIG. 11, control members 1010 may be positioned entirelyexternal to endoscopic device 1002. For example, control members 1010may be bundled into a sheath 1212, and sheath 1212 may extend along theexterior of endoscopic device 1002.

The systems shown in FIGS. 10 and 11 may be configured to operate in asimilar manner as set forth in step 502 of method 500 (FIG. 5). Forexample, the region of interest may be observed using an imaging device(e.g., endoscopic camera). Then, instead of deploying catheter 102 tothe region of interest, distal end 1003 of endoscopic device 1002 may beadvanced to the region of interest, where a respective expandable member(1006 or 1106) is expanded to position sensors 116 in contact withtissue. The system shown in FIGS. 12 and 13 also may operate in asimilar manner. For example, after visualization of the region ofinterest using the system of FIGS. 12 and 13, distal end 1003 ofendoscopic device 1002 may be extended distally of the region ofinterest, and then pulled proximally to the region of interest to causearms 1208 to move from the first, un-deployed configuration to thesecond, deployed configuration.

The systems shown in FIGS. 10-13 also may stabilize the endoscopicdevices on which they are deployed, and centralize the field of viewwithin the lumen being observed. These devices also may be used tostretch out folds within the observed lumen to improve visibility inareas that are difficult to see (e.g., around or within folds in thecolon and/or intestinal walls). These effects may improve diagnosticoutcomes. Yet another advantage of at least certain embodiments of thesedevices may be to free up the working port of the endoscopic device,enabling an operator to deploy other medical devices (for, e.g.,irrigation, hemostasis stabilization, suturing, tissue sampling, or thelike). Devices and methods of the present disclosure may help quantifythe severity of tissue damage or healing following treatment, improvingdiagnostic outcomes by making them less speculative. This may beparticularly relevant for inflammatory bowel diseases and ulcerativecolitis. Furthermore, at least certain embodiments of devices andmethods of the disclosure help improve diagnostic techniques by enablingthe measurement of perfusion and thickness in regions of interest. Thesemeasurements also help enable physicians to follow the progression oftreatment. Furthermore, it is contemplated that any of the inflatablemembers (e.g., balloons) described herein may be shaped such that, inone or more inflated configurations (including a fully inflatedconfiguration), the outer surface of the balloon contacts less than anentirety of a body lumen (e.g., 270 degrees or less, 180 degrees orless, 90 degrees or less around the lumen).

A medical device 1400 is shown in FIGS. 14-16. Medical device 1400extends from a proximal end (not shown) toward a distal end 1402.Medical device 1400 may have a relatively slim profile, and may be usedto measure tissue thickness in areas of the body that are not accessibleby larger devices. Medical device 1400 may include a diagnostic catheterwith at least a two-way steering mechanism. Such a catheter could bemade for deployment in a 3.7 mm working port of an endoscope so that itcan be visually placed at the region of interest, allowing fortangential tissue measurements.

Medical device 1400 includes a catheter 1403 and an optical sensor 1404disposed at or adjacent to distal end 1402. Catheter 1403 may be ahollow catheter having an open distal portion 1406 in which opticalsensor 1404 rests. A majority of catheter 1403 may have a circularcross-section. However, open distal portion 1406 may have a differentcross-section, such as, e.g., a half-moon shaped cross-section oranother suitable design that enables components of optical sensor 1404to be placed flush against tissue. Thus, optical components of opticalsensor 1404 may face radially outward from a side-facing surface ofcatheter 1403 (a surface that faces a direction perpendicular to alongitudinal axis of catheter 1403). Open distal portion 1406 mayinclude a distal and side facing opening of catheter 1403. Theside-facing portion of the opening may extend distally of the distalfacing opening.

Catheter 1403 also may include an articulating joint 1412. Controlcables (not shown) may be connected to a set of control knobs at theproximal end of medical device 1400, and to articulating joint 1412 tocontrol articulation of articulating joint 1412. By manipulating thecontrol knobs, an operator may be able to actuate, or bend, articulatingjoint 1412 during insertion and direct it to a region of interest.Catheter 1403 also may include an atraumatic tip 1414. For example, tip1414 may include a soft or flexible material to allow catheter 1403 tonavigate and traverse the tortuous pathways of a body in a generallyatraumatic manner.

A substrate 1435 a may be disposed at open distal portion 1406 ofcatheter 1403. Substrate 1435 a may include a flexible printed circuitboard (PCB) that is semi-rigid and that includes a stiffener. Componentsof optical sensor 1404 may be mounted on to substrate 1435 a. One ormore control wires 1435 c may extend proximally from optical sensor 1404to couple optical sensor 1404 to, e.g., power sources, computingdevices, and the like.

Optical sensor 1404 may include a photodetector 1437, and emitters 1436a, 1436 b, and 1436 c. Photodetector 1437 and emitters 1436 may besubstantially similar to detector 137 and emitters 136 set forth above.Each emitter 1436 a-c may be configured to radiate infrared light, oranother suitable wavelength. For example, some applications may benefitfrom infrared light, while other applications may benefit from otherwavelengths of light. For example, infrared light wavelengths maypenetrate deeper into tissue while visible light provides moreinformation regarding surface characteristics. Different wavelengthsreflect back de-oxygenated/oxygenated blood differently, and there areknown ratios that related to levels of oxygen, carbon dioxide and othercharacteristics in the tissue. While three emitters are shown in theembodiment of FIGS. 14-16, any other suitable number may be utilized.Photodetector 1437 and each of emitters 1436 a-c may be disposedlinearly along a same axis, such as, e.g., a longitudinal axis ofcatheter 1403. Exemplary dimensions of optical sensor 1404 are shown inFIG. 16. While certain values for each dimension are discussed below, itis contemplated that alternative dimensions also may be used. Substrate1435 may have a length 1602 (e.g., 15 mm), and a width 1604 (e.g., 3mm). A distalmost portion of photodetector 1437 may be disposed adistance 1606 (e.g., 1 mm) from a distalmost end of substrate 1435. Aproximalmost portion of photodetector 1437 may be disposed distances1608 (2 mm), 1610 (6 mm), and 1612 (10 mm) from distalmost portions ofemitters 1436 a, 1436 b, and 1436 c, respectively. It is contemplatedthat other suitable dimensions also may be utilized.

A lens 1438 may be disposed over optical sensor 1404 (includingphotodetector 1437 and each emitter 1436 a-c). Lens 1438 may isolateoptical sensor 1404 from tangential back scatter light between emitters1436 and photodetector 1437 from substrate 1435 a. Lens 1438 also mayprovide a barrier between tissue and the optical elements of opticalsensor 1404. The configuration of lens 1438 and optical sensor 1404 mayhelp enable medical device 1400 to determine tissue thickness in thebody with a relatively small profile and package. Lens 1438 may beformed from plastic, glass, or another suitable material.

Photodetector 1437 may be a square-shaped photodetector having sideswith a length of 2 mm, although other suitable shapes and dimensions arecontemplated. Each emitter 1436 may be a square-shaped emitter havingsides with a length of 1 mm, although other suitable shapes anddimensions are contemplated. In some implementations, a length of theflexible substrate is no more than 15 mm. In another embodiment, alength of the flexible substrate is no more than 11 mm.

Optical sensor 1404 may be coupled to a controller 1450 attached to asubstrate 1435 b that is substantially similar to substrate 1435 adescribed above. Controller 1450 may be disposed entirely within avolume contained within catheter 1403. When controller 1450 is disposedwithin catheter 1403, it may have a width less than 3 mm. Alternatively,controller 1450 may be disposed external to medical device 1400, inwhich case, the control wires from controller 1450 to optical sensor1404 may be attached to a flexible extension of the device.

Controller 1450 may be configured to direct and source constant currentfor each emitter 1436 a-c separately, but not simultaneously, as thedata acquisition may be time multiplexed during a sampling cycle. Inother words, at any given time, only one of emitters 1436 a-c may emitlight. The current setting for each emitter 1436 a-c may change due tothe spatial diversity from photodetector 1437, and may be adjustedduring a calibration process. Photodetector 1437 may require control ofan amplification device. Since photodetector 1437 may be mostlycapacitive, a trans-impedance amplifier may be used for the analoginterface.

The spatially diverse optical sensor 1404 may be driven through threetime division slots to activate each emitter 1436 a-c separately, with afourth time slot allowing for data acquisition when none of the emitters1436 a-c is activated. This fourth time slot enables the sampling ofambient light. If an operator is confident that the area being measuredhas no ambient light, then the fourth time slot may be skipped to reduceprocedure time. This sequence is shown in FIG. 17. The acquisition ofsamples may be timed sequentially to enable each emitter 1436 a smallperiod of on-ramp to allow for wavelength and temperature stabilizationbefore a measurement is obtained by photodetector 1437. Suggested sampletimes could be from 50 microseconds to 200 microseconds per dataacquisition. A sample period may include the complete cycle of all fourperiods, and may impact the overall sample rate of the signal dataacquisition.

For tissue thickness measurements, 50 samples per second may beadequate, allowing for a total sample period of 20 milliseconds. Thiswould allow for 200 microsecond emitter (LED) sampling. In order toincrease data fidelity, the sample period may be increased to, e.g., upto 200 samples. In this case, the total sampling period for all fourchannels is 500 microseconds, allowing for emitter sampling of about 100microseconds. A longer emitter sampling period allows for a more refineddynamic range of the analog sampling through photodetector 1437 withlower emitter current being supplied (similar to more exposure time inphotography for a lower light setting).

The analog data provided by the amplifier after sampling each emittermay be converted to digital format for further processing. Thisdisclosure contemplates any suitable type of analog to digital converter(ADC). The accuracy of the ADC may be at least comparable to an 8-bit orgreater ADC to meet the measurement requirements of the applicationscontemplated by this disclosure.

The medical devices described with respect to FIGS. 14-17 can enable theuse of emitters using a centroid wavelength of approximately 940 nm(e.g., 930-950 nm) arranged linearly apart from one another to collect adiffusion gradient of reflected and absorbed light in tissue. Evaluationof the gradient makes use of a slopes-ratio method to correlatemeasurements made by photodetector 1437 with tissue thickness. The ratiocomprises three different vectors coming from three LED emitters (e.g.,emitters 1436 a-c) relative to a fixed photodiode (e.g., photodetector1437). Considering the distance of the emitters 1436 a-c fromphotodetector 1437, emitter 1436 a is the closest to photodetector 1437at a distance of two mm, emitter 1436 b is mid-range relative tophotodetector 1437 at a distance of six mm, and the furthest is emitter1436 c at a distance of ten mm relative to photodetector 1437.

Tissue thickness may be determined based on data collected byphotodetector 1437. For example, a ratio of slopes method can be usedfor evaluating the short, mid and long reflective distances as shown inthe formula below:

$T_{ratio} = \frac{{1436a} - {1436b}}{{1436a} - {1436c}}$

In the above equation, 1436 a, 1436 b, and 1436 c represent valuesmeasured by photodetector 1437 in response to emissions from emitters1436 a, 1436 b, and 1436 c, respectively. This equation is used furtherin the linear model described below.

The use of different wavelengths may provide an ability to measuredifferent skin depths. Infrared light, for example, may provide betterskin depth penetration than some of the wavelengths in the visiblespectrum. Other wavelengths offer different optical properties in livetissue, and may be used for other characteristics and still providethickness measurements. Empirical results from a study show slightvariations in early results using simulated tissue phantoms. The basisof certain results are from fabricated models. In a lab setup, differentwavelengths were evaluated to determine different absorption andreflection patterns.

A fitted line for linear model statistical regression from datacollected with an exemplary device similar to the device described byFIGS. 14-16 is shown below.

Coefficients:

TABLE 1 Statistical Curve for Collected Data Estimate Standard Error tvalue Pr(>|t|) Intercept 0.891731 0.011087 80.434 1.43E−07 Thickness−0.017409 0.002181 −7.982 0.00134

Table 1 illustrates how well the regression fits in the data. Intercept(b) and thickness (m) estimates are the coefficients for scalingaccording to the collected data. The significance codes are a functionof the R utility to give a approximation of how valid the probability ofthe null hypothesis tested is. The smaller the Pr value, the higher thesignificance. When significance is higher, the mathematical outcomebeing evaluated is higher.

The residual standard error was 0.0128 on four degrees of freedom. Themultiple R-squared was 0.9409, and the adjusted R-squared was 0.9262.The F-statistic was 63.71 on one and four degrees of freedom, and thep-value was 0.001335. The correlation value was −0.9700123, whichmeasures the linear relationship between two variables. In this case,there is a negative correlation between the IR slope value and tissuethickness. As the thickness increases, IR slope value decreases (i.e.,they are inversely related to each other). Both of the p-values werebelow 0.05 thresholds, and thus, this model was statisticallysignificant.

Model Fitted Values

TABLE 2 shows the delta between the real values collected for eachthickness measurement and the related curve fit plot. Actual IRThickness Values Fitted IR Values 1.6 0.869627 0.8638776 2.5 0.8586040.8482098 3.0 0.834698 0.8395055 4.9 0.789127 0.8064291 6.4 0.7739790.7803161 8.5 0.756061 0.743758

Linear Model

Y=0.891731 −0.017409X

The R-squared value was 0.9409. 94 percent represents the proportion ofvariation in the response variable. Thus, as tissue thickness increases,the IR slope value decreases.

The linear model is shown in FIG. 18, which is a fitted line plotregression analysis of this experiment in an SIG lab with phantomoptical equivalent tissue models using slopes ratios methods.

One example translation with this dataset is:

${{Thickness}\; ({mm})} = \frac{R - T_{ratio}}{k}$

Where R is the intercept (0.8917 in this example) and k (0.01741 in thisexample) is the slope (negative) derived from experimental data.

The relatively slim profile of medical device 1400 also may enableinternal placement of medical device 1400 though a scope using directvisualization methods. Medical device 1400 may be used to access manyregions of interest in the intestinal tract (e.g., esophagus, stomach,large intestines, duodenum, and parts of the small intestines). In otherexamples, medical device 1400 may be used to measure thickness in aregion of interest, which can then be used as a datapoint to helpquantify the severity of healing or inflammation. The data can be partof an index if used with other measurements, such as, e.g., changes inperfusion, temperature, microvascular changes for severity scoring andhealing of the tissue of interest. Furthermore, because optical sensor1404 is flat, it may be used to determine tissue thickness when placedexternal to a patient, such as, for example, against the skin of apatient.

Those skilled in the art will understand that the medical devices setout above can be implemented in any suitable body lumen (e.g., bloodvessels, the biliary tract, urological tract, gastrointestinal lumens,and the like) without departing from the scope of the disclosure asdefined by the claims. In particular, constructional details, includingmanufacturing techniques and materials, are well within theunderstanding of those of skill in the art and have not been set out inany detail here. These and other modifications and variations are wellwithin the scope of the present disclosure and can be envisioned andimplemented by those of skill in the art.

Other implementations of the present disclosure will be apparent tothose skilled in the art from consideration of the specification andpractice of the implementations disclosed herein. It is intended thatthe specification and implementations be considered as examples only,and departures in form and detail may be made without departing from thescope and spirit of the present disclosure as defined by the followingclaims.

1-19. (canceled)
 20. A medical device, comprising: a catheter; anoptical sensor disposed at or adjacent to a distal end of the catheter,the optical sensor including a photodetector and one or more emitters,the photodetector and each of the one or more emitters of the opticalsensor being disposed linearly along a longitudinal axis of thecatheter; and a controller disposed within the catheter, the controllerbeing configured to determine a thickness of tissue adjacent to theoptical sensor based on input from the optical sensor.
 21. The medicaldevice of claim 20, wherein the catheter includes a circularcross-section along a proximal portion of the catheter, and asemicircular cross-section along a distal portion of the catheter. 22.The medical device of claim 21, wherein the distal portion of thecatheter includes a planar side surface and a rounded side surface, withthe optical sensor disposed on the planar side surface such that thephotodetector and the one or more emitters are positioned flush relativeto one another on the distal portion.
 23. The medical device of claim22, wherein the one or more emitters are configured to collect adiffusion gradient of reflected and absorbed light in the tissueadjacent to the optical sensor.
 24. The medical device of claim 23,wherein the controller is configured to correlate measurements of thegradient of reflected and absorbed light with tissue thickness via aslope-ratio.
 25. The medical device of claim 24, wherein each of the oneor more emitters is positioned along the planar side surface at varyinglinear distances from the photodetector; wherein the slope-ratio is atleast partially based on the linear distances of each of the one or moreemitters from the photodetector and the diffusion gradient collected byeach of the one or more emitters.
 26. The medical device of claim 21,wherein the catheter includes a substrate disposed over the distalportion, wherein the substrate includes a flexible printed circuitboard, and the optical sensor is mounted on the substrate.
 27. Themedical device of claim 26, further including a lens disposed over theoptical sensor, wherein the lens is configured to isolate thephotodetector and the one or more emitters from tangential back scatterlight between emitters and photodetectors from the substrate.
 28. Themedical device of claim 27, wherein the lens is configured to isolatethe photodetector and the one or more emitters from the tissue adjacentto the optical sensor.
 29. The medical device of claim 26, wherein thecontroller is mounted on the substrate and positioned flush with thephotodetector and the one or more emitters.
 30. The medical device ofclaim 20, wherein the controller is configured to active each of the oneor more emitters during a time slot that is separate from one another;wherein the controller is configured to separately direct current toeach of the one or more emitters such that only one of the one or moreemitters emits light during the time slot.
 31. The medical device ofclaim 30, wherein the controller is configured to acquire a plurality ofdata samples, with each of the plurality of data samples including lightdetected by the photodetector during each of the time slots for the oneor more emitters.
 32. The medical device of claim 31, wherein theplurality of data samples acquired by the controller ranges from about50 data samples to about 200 data samples when determining the thicknessof tissue adjacent to the optical sensor.
 33. A medical device,comprising: a catheter having a proximal end and a distal end; anoptical sensor at the distal end of the catheter, the optical sensorincluding a photodetector and a plurality of emitters, the photodetectorand each of the plurality of emitters are positioned in a lineararrangement relative to one another; and a controller configured todetermine a thickness of tissue positioned adjacent to the distal endbased on input from the optical sensor.
 34. The medical device of claim33, wherein the distal end of the catheter includes a half-moon shapedprofile with a rounded side and a planar side, with the optical sensormounted to the planar side.
 35. The medical device of claim 33, whereinthe plurality of emitters are configured to collect a diffusion gradientof light from the tissue positioned adjacent to the optical sensor, andthe controller is configured to correlate measurements of the gradientof light with tissue thickness via a slope-ratio.
 36. The medical deviceof claim 35, wherein the slope-ratio is at least partially based on adistance between each of the plurality of emitters from thephotodetector and the diffusion gradient collected by each of theplurality of emitters.
 37. The medical device of claim 33, wherein thecontroller is configured to direct current to each of the plurality ofemitters during a separate time slot such that only one of the pluralityof emitters emits light during each time slot.
 38. The medical device ofclaim 37, wherein the controller is configured to acquire samples basedon light detected by the photodetector during each of the time slots.39. A medical device, comprising: a catheter including a proximal endand a distal end; an optical sensor at the distal end of the catheter,wherein the optical sensor is movable relative to the proximal end ofthe catheter, the optical sensor includes at least one photodetector andat least one emitter that are aligned linearly relative to one anotheralong the distal end of the catheter; and a controller in communicationwith the optical sensor, the controller is configured to determine athickness of tissue detected adjacent to the distal end of the catheterbased on light detected by the optical sensor.